Abstract

Recent observations of carbon, sulphur and titanium isotopes at redshifts z∼1 and in the local stellar disc and halo have opened a new window into the study of isotopic abundance patterns and the origin of the chemical elements. Using our Galactic chemical evolution code getool, we have examined the evolution of these isotopes within the framework of a Milky Way-like system. We have three aims in this work: first, to test the claim that novae are required, in order to explain the carbon isotope patterns in the Milky Way; secondly, to test the claim that sulphur isotope patterns at high redshift require an initial mass function (IMF) biased towards massive stars; and thirdly, to test extant chemical evolution models against new observations of titanium isotopes that suggest an anti-correlation between trace-to-dominant isotopes with metallicity. Based upon our dual-infall galactic chemical evolution modelling of a Milky Way-like system and the subsequent comparison with these new and unique data sets, we conclude the following: novae are not required to understand the evolution of 12C/13C in the solar neighbourhood; a massive star-biased IMF is consistent with the low ratios of 12C/13C and 32S/34S seen in one high-redshift late-type spiral, but the consequent super-solar metallicity prediction for the interstellar medium in this system seems highly unlikely; and deficient isotopes of titanium are predicted to correlate positively with metallicity, in apparent disagreement with the new data sets; if confirmed, classical chemical evolution models of the Milky Way (and the associated supernovae nucleosynthetic yields) may need a substantial overhaul to be made consistent.